The Financial Supervisory Service (FSS) is waiting to hear from Citibank Korea Inc and Standard Chartered Bank Korea Ltd about the internal probes before deciding whether to conduct its own investigation, Lee Sang-koo, director-general of the agency’s bank supervision team, said by phone yesterday.

The FSS may begin inspecting the two banks regarding the allegations, the Seoul Economic Daily reported, without citing anyone.

The South Korean prosecutors’ office said in a Dec. 11 statement it arrested an employee of “Bank C” for leaking information on 34,000 clients, including details of lending contracts.

Citibank Korea confirmed in an e-mail yesterday that it was “Bank C.” The Seoul-based unit conducted its own investigation at the FSS’ request following the arrest, it said, without elaborating on the results of the probe.

The prosecutors’ office also arrested a worker from an information technology company contracted to a lender identified only as “Bank S” for stealing 104,000 clients’ information, according to the Dec. 11 statement.

The data was sold at up to 500 won (US$0.47) per piece of client information, the statement said.

The leaks were the “biggest ever” incurred by banks, prosecutors said.

Standard Chartered and Citigroup have seen their US$6 billion bet on South Korea turn sour in less than 10 years, as the two banks struggle to sustain profits in an economy plagued by rising household debt.

Standard Chartered took a US$1 billion writedown on the value of its business in the country in August, a cost that is set to end the London-based lender’s 11-year streak of record annual profits.

At Citigroup, South Korea will hurt revenue in Asia through next year, chief financial officer John Gerspach has said.

South Korean lenders have seen their return on equity (ROE), a measure of profitability, shrink by more than half over the past decade when Standard Chartered and Citigroup first pledged the largest-ever foreign investment in the country’s financial industry. With the government stepping up efforts to curb household debt, foreign banks have been left seeking ways to cut costs.

“Banks will have to accept the new normal of low growth, low return on equity,” said Yoo Sang-ho, a Seoul-based banking analyst at HI Investment & Securities Co. “They have to forget what they saw in the mid-2000s.”

Over the past five years, South Korean economic growth slowed to 2.9 percent from an average 5.8 percent in the nine years through 2008, according to the IMF, as household debt swelled.

At the same time, commercial banks saw their return-on-equity slump to about 7.4 percent last year from 20.3 percent in 2005, FSS data showed.

South Korean President Park Geun-hye, who took office in February, has pledged to ease consumer debt burdens by restructuring loans for low-income earners. The move follows measures already in place since 2006 limiting the amount people can borrow depending on their income and home values. In 2011, the financial regulator asked banks to provide more fixed-rate loans to reduce risks from increases in interest rates.